The proposal is a study of the basic biochemical control of serine biosynthesis in vivo. The project may be subdivided into three parts: 1) The purification and detailed kinetic analysis of the enzymes of the phosphorylated pathway of serine synthesis; D-3-phosphoglycerate dehydrogenase, phosphoserine aminotransferase and phosphoserine phosphatase; 2) The determination of the equilibrium constants under physiological conditions for the reactions of the non-phosphorylated pathway of serine biosynthesis: D-glycerate dehydrogenase and hydroxypyruvate amionotransferase; and 3) The determination in tissue extracts of key intermediates in the pathway of serine synthesis: D-3-phosphoglycerate, phosphoserine, serine, 2-phosphoglycerate, phosphate, alanine, gdutamate, 3-hetoglutarate, malate, lactate, pyruvate, and oxaloacetate.